The present invention relates in general to transmission shifters, and, more specifically, to a bushing for mounting a shifter reaction arm to a transmission housing.
Gear selection for manual transmissions is typically implemented using a shift lever mounted to a shifter housing for manipulation by an driver according to a shift pattern. A shift linkage is connected between the shift lever and a transmission selector rod that physically moves the transmission operation from one gear to another. The shifter housing is typically connected to the vehicle body and to the transmission housing. One or more reaction arms typically connects the front of the shifter housing to the transmission housing via a bushing.
In order to ensure smooth gear selection, movement of the shift linkage (e.g., rotation of a selector rod) must be within a predefined angular range. If rod rotation is outside this range, an attempted gear selection can result in grinding or clashing or the wrong gear may be selected. Typically, the accuracy required for positioning the shift linkage necessitates maintaining an orientation of the shift housing which varies by no more than about 1.5° of rotation around its forward axis (i.e., parallel to the shift linkage).
Vibrations from the vehicle powertrain may be coupled into the shifter housing through either the mountings to the body or transmission housing, resulting in undesirable noise and vibration at the shift lever and into the shift knob/handle. The more significant path for noise and vibration propagation is via the front connection of the reaction arm(s) to the transmission case.
Relatively soft, compliant attachments to the shifter housing can reduce noise and vibration but also results in less control over the exact relative positions of the shifter components and transmission. In order to reduce the propensity for rotational movement of the shifter housing, dual reaction arms can be used to connect the shifter housing with the transmission housing. Spaced, parallel arms increase resistance against any rotational torque applied to the shifter housing (e.g., manual forces when shifting the shift lever according to the shift pattern). With dual reaction arms, rotation may be sufficiently reduced to permit the use of relatively soft rubber bushings at the connection points of the reaction arms to the transmission housing. However, dual reaction arms increase the packaging space, weight, and cost for the shifter.
A single reaction arm may be preferred in order to reduce packaging space, weight, and cost. However, a relatively stiffer bushing has been required in order to avoid rotation which can interfere with gear shifting. Consequently, noise and vibration transmitted to the shift lever are increased. It would be desirable to improve isolation of vibrations across a bushing connection while simultaneously limiting rotation of the reaction arm.